This invention relates generally to aluminum alloys and more particularly to aluminum-titanium alloys produced using powder metallurgy techniques.
Advanced aircraft require utilization of materials which are not only lightweight but retain structural strength at temperatures between 150.degree. C. and 300.degree. C. State-of-the art elevated temperature aluminum alloys currently used for this application are composed of large quantities of transition elements, such as Fe, Mo and V. These elements form thermally stable intermetallics in the aluminum which resist coarsening because the elements have low solid state solubilities and low diffusivities. However, such heavy transition elements increase the alloy's density, an undesirable effect.
Titanium, on the other hand, is relatively lightweight and is currently used in small quantities (0.01-0.20 wt. %) as a grain refiner in cast and wrought aluminum alloys. However, alloys containing .gtoreq. 0.5 wt. % titanium have not been used for structural applications such as aircraft because conventional casting techniques result in a microstructure consisting of coarse Al.sub.3 Ti particulates embedded in the aluminum matrix. These large intermetallics degrade the strength and ductility of the aluminum.
Rapid solidification technology is a well-known powder metallurgy technique which provides unique structures, morphologies, and metastable phases. It has been used to create aluminum alloys using transition elements, resulting in the desired fine microstructure. Rapid solidification has not been successfully used in the presence of carbon, however because the carbon is virtually insoluble in the aluminum and agglomerates before the process can be completed. It is therefore not possible to produce carbides using rapid solidification processing alone.
Mechanical alloying is another well-known powder metallurgy technique which involves the process of repeatedly fracture-and-cold welding a powder to produce a strong atomistic bond between unlike elements. Aluminum alloys produced using this technique have excellent high temperature mechanical properties due to the fine dispersion of aluminides, carbides, and oxides distributed in their microstructures. Mechanical alloying has been attempted using elemental aluminum and titanium powders and reasonable mechanical strength was obtained but ductility suffered. This was caused by the presence of large Al.sub.3 Ti intermetallics and alloy inhomogeneity. Mechanical alloying alone can not refine and homogenize the size and distribution of Al.sub.3 Ti.
No attempt has been made to combine the processes of rapid solidification and mechanical alloying, because the benefits of doing so have not become apparent.